The continuous reduction in reserves of fossil fuels (coal, oil, and natural gas) and the environmental pollution caused by use of fossil fuel directly threaten the survival and development of the human race. Thus, various countries' attentions are being paid to the development of renewable and environment-friendly energy.
Bio-mass is an organic material derived through photosynthesis of a plant. Since bio-mass is widely distributed and used, is cleaner than fossil fuel, and generates no CO2, bio-mass attracts much attention as an important renewable energy. Bio-mass can be converted into synthetic gas or liquefied fuel through such a method as thermal chemistry or biochemistry, and can be applied to power generation, industrial fuel, or chemical industry products. Thus, bio-mass may replace a considerable amount of fossil fuel without changing the existing energy conversion systems. Therefore, bio-mass is being preferentially developed by various countries.
Bio-mass may be converted into synthetic gas or liquefied fuel through various kinds of methods, and the bio-mass gasification technology is viable for a larger number of types of available bio-masses and has greater expandability than other technologies.
The gasification process for bio-mass is performed through a thermal-chemistry conversion process in which a solid bio-mass material and a gasification agent (air, oxygen, vapor, or carbon dioxide) produce a chemical reaction under a high-temperature condition such that the solid bio-mass material is converted into a gas mixture based on hydrocarbon containing carbon, hydrogen, and oxygen. The gas mixture is typically referred to as synthetic gas.
The composition of the synthetic gas generated during the gasification process may be primarily influenced by the material characteristics of the bio-mass used during the gasification process, and differ depending on the type of the gasification agent, the type of a gasifier, and the reaction condition of temperature and pressure. The basic purpose of gasification is to obtain a desired synthetic gas composition, reduce the content of tar oil during the gasification, and maximize the gasification efficiency of the system, the carbon conversion rate, and the content of CO and H2 in the synthetic gas.
In order to accomplish the above-described purpose, an entrained-flow flow gasifier and a fluidized-bed gasifier are provided.
The entrained-flow gasifier sprays pulverized fuel in several tens to hundreds of m with an oxidizing agent so as to form a high-temperature combustion zone at 1,600 degrees or more, and injects a large amount of pulverized fuel around the high-temperature combustion zone so as to perform gasification. The entrained-flow gasifier is mainly utilized for gasifying coal which may be easily pulverized, but bio-mass, bio-mass char, and pre-processed high water content bio-mass (dried sewage sludge) may be pulverized and utilized. Since the entrained-flow gasifier has a simple structure, the entrained-flow gasifier may be easily applied to a pressurized gasification system which can be operated at high pressure.
The fluidized-bed gasifier may use fuel in several mm to several cm, and use sand as a heat medium and a fluidizing material. Thus, the fluidized-bed gasifier is utilized for gasifying a waste material having various properties and a low heat value (or a significant variation in heat value), bio-mass, and low-grade coal which cannot be utilized as pulverized fuel.
In order to operate the fluidized-bed gasifier, gas with a predetermined pressure, a predetermined flow rate, and a predetermined temperature or more is required for fluidization, and a fluidized-bed gasification agent is supplied through a distributor so as to perform gasification.
The synthetic gas generated from the gasification system is refined and used as fuel or utilized for producing a chemical material through a catalyst conversion process. During this process, it is necessary to treat tar, unburned matter, or dust which may be formed within the synthetic gas.
During the refining process, however, the synthetic gas is cooled down. At this time, sensible heat escaping during the refining process may be reused through waste heat recovery, but waste heat recovery efficiency is not very high.